Catalog Search Guide
You can search our catalog using different mineral attributes. For example, you can search by color such as green, yellow or purple, or by chemical elements such as uranium, calcium or iron, or by mineral groups such as phosphate, silicate or carbonate. You can also filter by crystal habit like crystal, geode or crystal on matrix, by specimen size such as thumbnail, small, medium or cabinet, and by features such as radioactive or fluorescent minerals.
Gypsum
Gypsum is a soft, widespread evaporite mineral composed of hydrous calcium sulfate (CaSO₄·2H₂O), forming in alkaline lake muds, salt flats, clay beds, evaporated seas, and caves. With a Mohs hardness of only 1.5–2, it is soft enough to scratch with a fingernail, yet its crystal habits are among the most varied and collectible in mineralogy. The species includes several classic varieties prized by collectors: selenite, the clear, glassy, prismatic form; satin spar, with its silky fibrous sheen; alabaster, a fine-grained massive variety long used for carving; and the sculptural desert rose, rosette clusters of bladed crystals studded with trapped sand grains. Pure gypsum is colorless to white, but iron oxides and clay impurities can tint specimens yellow, brown, red, orange, or gray.
The type locality for record-breaking gypsum is the Naica Mine in Chihuahua, Mexico, where the legendary Cueva de los Cristales (Cave of the Crystals) yielded selenite blades reaching over 11 meters long and weighing up to 55 tons, grown over hundreds of thousands of years in a stable, near-58°C hydrothermal environment. Nearby Santa Eulalia, also in Chihuahua, has produced outstanding transparent selenite crystals, while Saltillo, Coahuila supplies much of the desert rose material reaching the mineral market. Beyond Mexico, Morocco is a leading global source of selenite, mined near the Atlas Mountains and fashioned into towers, spheres, and lamps, as well as sand-embedded desert roses. Classic American localities include the Great Salt Plains of Oklahoma, famous for hourglass-included selenite and sand-crystal specimens, plus Ellsworth (Ohio), Hanksville (Utah), Lockport (New York), and the Mammoth Caves of Kentucky, known for curved gypsum flowers. Other notable occurrences span Algeria, Tunisia, Australia, Peru, Spain, England, Poland, Russia, and Canada's Red River Floodway near Winnipeg, which yields fine yellow crystals.
Collectors seek gypsum for the extraordinary diversity within a single species — from water-clear selenite blades with sharp rhombic terminations and arrowhead twins, to chatoyant satin spar, to the geometric charm of desert roses. Gypsum frequently occurs alongside calcite, dolomite, limestone, halite, and anhydrite, into which it converts under dehydration and heat. Its combination of remarkable crystal size potential, worldwide distribution, striking transparency, and low cost of entry makes gypsum a favorite for both beginner and advanced mineral collections, offering specimens that range from delicate cave-grown flowers to museum-scale giant crystals.
